B. Kirschleger

Réactivité d'organozinciques allyliques β-fonctionnels γ-substitués. Préparation d'α-méthylène γ-butyrolactones β- et γ-substituées

Abstract Stable organozinc compounds derived from alkyl 3-alkyl-2-(bromomethyl) propenoates reacted with ketones and aldehydes to give α-methylene γ-butyrolactones in excellent yields. Different reaction parameters were studied and some transition states were proposed.

LA REACTION DE WITTIG-HORNER EN MILIEU HETEROGENE IV: PERFORMANCES COMPAREES DE BASES FAIBLES TELLES QUE K2CO3 ET KHCO3 DANS L'EAU OU DES SOLVANTS ANHYDRES

Abstract The Wittig-Horner reaction has been explored with phosphonates , CO[sbnd]R2, CN) with K2CO3 or KHCO3 as bases in water or anhydrous solvents such as THF, toluene and CH2Cl2, with or without phase-transfer catalysis. The scope and limitations of these procedures, which can give excellent yields (75–100%), have been compared. Olefins are formed with E geometry for A = COOEt, CO[sbnd]R2 (R′ [dbnd] H) and as mixtures of E/Z compounds for A [dbnd] CN. Side reactions (i.e. crotonization, isomerization, saponification, Knoevenagel and Cannizzaro reactions) can be eliminated using reaction conditions modified for each case. Optimum times and temperatures of the reactions have been determined for improved yields. The use of a two phase liquid-liquid system in water without solvent often gives excellent yields (A [dbnd] COOEt, COR2, CN). However, benzaldehyde gives almost quantitative yields (A [dbnd] COOEt) in a solid-liquid heterogenous medium in boiling toluene using solid K2CO3 or KHCO3, with or withou...

Synthesis of various 2H-benzopyran compounds and their kinetic resolution by asymmetric hydrolysis of their racemic acetates mediated by lipases

The preparation of 2H-benzopyrans from bromophenols and tertiary allylic alcohols is described. The reaction is characterised by its mildness, good yields and ease of work-up. Kinetic resolution of the latter up to 95% ee was obtained by using enzyme-catalysed enantioselective hydrolysis. # 2000 Elsevier Science Ltd. All rights reserved.

Préparation et étude de nouveaux dérivés organozinciques allyliques fonctionnels

Abstract Stable organozinc compounds derived from alkyl-3-alkyl-2-(bromomethyl)-proenoates have been prepared. NMR 13 C, 1 H and IR stidies show only one Z stereoisomer (no methylenic form) with a strong chelation between zinc and the carbonyl oxygen of the ester and solvated by only one solvent molecule. Hydrolysis can be achieved by two concurrent mechanisms with or without transposition.

High Yield Synthesis of α Propargylic Acrylic Ester: A General Access to α Substituted Acrylic Esters

Abstract A heterogeneous mediated, high yield, monopropargyla-tion of ethyl benzoylacetate followed by a methyle-nation reaction using a formaldehyde addition-benzoyl elimination mechanism is described. This useful method is extended to the synthesis of a substituted acrylic esters.

Enantioselective Synthesis of Cordiachromene

An enantioselective synthesis of cordiachromene is described. An allylic alcohol moiety is first attached in the o-position to the methoxymethoxy substituent in 1-methoxy-4-methoxymethoxybenzene. Then chirality is introduced successively through asymmetric Sharpless epoxidation on the allylic alcohol moiety and regioselective ring-opening. The chiral diol prepared is then cyclized to chromanmethanol with total retention of configuration. Chromenemethanol is obtained after bromination and dehydrobromination. The total synthesis is achieved by reaction between the tosylated chromene chiral moiety and an organomagnesium prenylated compound.

Une methode tres simple et reproductible de dosage des solutions etherees de LiAlH4

A new, simple method is described for the accurate titration (reproducibility ± 2%) of a solution of LiAlH4 in diethyl ether. It is based on the reaction of benzyl alcohol with the deep-violet complex formed between LiAlH4 and 1,10-phenanthroline in THF in the presence of magnesium salts.

α-Monohaloalkyllithiums non fonctionnels

Zusammenfassung New stable monohalocarbenoids RCXLiCH3 (X = Cl, Br; R = H, CH3, alkyl are prepared by bromine-lithium exchange from the corresponding bromohaloalkanes RCXBrCH3 and s-butyllithium in the presence of one equivalent of lithium bromide at −115°C in a mixture of THF/Et2O/pentane. These carbenoids are treated with carbonyl compounds and give epoxides at −90°C (X = Br). Epoxidation is activated by the presence of LiBr (electrophilic activation).

Formation et stabilité des carbénoïdes monohalogénés β-éthers

Abstract The β-alkoxy monohalogenated carbenoids, C 6 H 5 CH(OSiMe 3 )CHXLi, can be obtained by bromine-lithium exchange from the corresponding bromohaloether in the presence of s-butyllithium in a mixture of THF / ether / pentane at −130°C. The stability of the carbenoid (α-elimination and β-elimination) is described and discussed.

Expeditious preparation of various Δ9-6a,10a cis and trans 2-substituted tetrahydrocannabinoids

The one-step preparation of various cis and trans 2-substituted tetrahydrocannabinoids (Δ9-THC) from aryl tertiary allylic alcohols is described. The reactions are characterized by their mild conditions, good yields and ease of work-up.